1. Field of the Invention
The present invention relates to an optical system in a laser beam machining device of a type used to cut the workpiece intermittently and also to a laser beam machining method using the laser beam machining device.
2. Description of the Prior Art
In general, lead or lead alloy used in, for example, lead electrodes for a lead storage battery is low in hardness, but high in viscosity. When it comes to the cutting of metal having a low hardness and a high viscosity, the use of a shearing technique often result in the formation of burrs in the cut face of the metal. On the other hand, where a laser cutting technique is employed, the metal can be precisely cut at an increased cutting speed with little loss of material and with no substantial formation of burrs on the cut face.
In the practice of the laser cutting technique, a laser beam emitted from a laser oscillator is condensed by a condenser lens so as to converge at a point where a nozzle is positioned for blowing an assist gas to facilitate cutting. If the assist gas employed is oxygen, oxidation of the metal in contact with the oxygen can be effectively utilized to facilitate the metal cutting and, therefore, the power of the laser may be reduced to only a fraction of the laser power necessitated when only the laser beam is used with no assist gas employed. Specifically, at an initial stage of the laser cutting, fusion of the metal requires a relatively large quantity of energy in the laser beam. However, once the metal is heated to a predetermined temperature equal to or higher than the melting point, in an extreme case, the blow of oxygen would suffice to accomplish the cutting with no laser beam radiation needed. Also, the oxygen so blown onto the metal is effective to remove molten metal to facilitate the continued cutting.
In view of the foregoing, it is a general notion that, when it comes to the cutting of a metal by the use of the laser beam, the combined use with the laser an beam of energy density sufficient to cause the workpiece to be heated to a required temperature with oxygen as the assist gas is preferred at the initial stage of cutting.
Reference to FIG. 2 of the accompanying drawings will now be made for a detailed discussion of the prior art laser cutting method as applied to the laser beam cutting of a workpiece into a plurality of generally rectangular pieces such as, for example, lead electrodes used in a lead storage battery, with discontinuous radiation of a laser beam. As shown, referring to FIG. 2, reference numeral 17 designates a generally grid-patterned sheet of lead electrodes for use in a lead storage battery; reference numerals 18, 19, 20 and 21 designate respective condenser lenses positioned in the vicinity of associated cutting portions; and reference numerals 22, 23, 24 and 25 represent respective cutting nozzles positioned in alignment with the corresponding condenser lenses 18 to 21 for supplying an assist gas therethrough towards the lead electrode 17 sheet. Reference numerals 26, 27, 28 and 29 designate respective beam oscillators for emitting laser beams therefrom, which beams are subsequently deflected by associated deflecting mirrors 30, 31, 32 and 33 so as to travel towards the corresponding condenser lenses 18 to 21. When all four beam oscillators 26 to 29 are excited simultaneouly, laser beam cutting at four locations can be accomplished.
The prior art laser beam cutting method discussed above has a problem in that, if the laser beams are continuously radiated towards portions of the sheet being cut which are not required to be cut by the laser beam, i.e. cut by the oxygen blowing, the laser beams tend to be used unnecessarily. Also, the prior art laser beam cutting method requires the use of a number of beam oscillators equal to the number of cutting lines along which cutting is desired to be made, the apparatus as a whole tends to become bulky in size and expensive.